Women, and even men, currently have a tendency to wish to look youthful for as long as possible and consequently seek to fade out the signs of age on the skin, which are reflected in particular by wrinkles and fine lines. In this respect, advertising and the fashion world talk about products intended to keep the skin radiant and wrinkle-free, which are signs of youthful skin, for as long as possible, and all the more so since the physical appearance has an effect on the psyche and/or on the morale.
Up until now, wrinkles and fine lines were treated using cosmetic products containing active agents acting on the skin, for example by improving its cell renewal or alternatively by promoting the synthesis of, or by preventing the degradation of, the elastic fibres of which skin tissue is composed.
Although these treatments make it possible to act on the wrinkles and fine lines caused by chronological or intrinsic aging, and also on those caused by photoageing, they have no effect on expression wrinkles, which require an intervention on the muscular contractile component (via muscle-relaxing agents) or dermal contractile component (via dermo-decontracting agents) of wrinkles.
Expression wrinkles are in fact the result of mechanisms that are different from those that generate wrinkles caused by aging.
Specifically, they are produced due to the effect of the strain exerted on the skin by the skin muscles that allow facial expressions. Depending on the shape of the face, the frequency of facial expressions and possible tics, they may appear as early as childhood. Age, along with certain environmental factors such as exposure to sunlight, are not involved in generating them, but may make them deeper and permanent.
Expression wrinkles are characterized by the presence of grooves around the orifices formed by the nose (nasal grooves), the mouth (perioral wrinkles and “sour-face” wrinkles) and the eyes (crow's-feet wrinkles), around which are the skin muscles, and also between the eyebrows (glabella wrinkles or lion wrinkles) and on the forehead.
Until now, the only means commonly used for acting on expression wrinkles is botulinum toxin, which is in particular injected into the wrinkles of the glabella, which are wrinkles between the eyebrows (see J. D. Carruters et al., J. Dermatol. Surg. Oncol., 1992, 18, pp. 17-21).
The applicant has also proposed various compounds capable of providing a muscle-relaxing effect when they are applied topically to the skin, thus making it possible to act on expression wrinkles via another route. Among these compounds, mention may in particular be made of calcium channel-associated receptor antagonists, such as verapamil (FR-2 793 681), and in particular manganese and its salts (FR-2 809 005), and alverine (FR-2 798 590); chloride channel-associated receptor agonists, including glycine (EP-0 704 210) and certain extracts of Iris pallida (FR-2 746 641); and sapogenins (EP-1 352 643).
Along with these muscle-relaxing agents, the applicant has described various dermo-decontracting compounds, and in particular amine compounds (EP-1 405 633).
However, there is still a need for compounds that are more effective than those of the prior art for smoothing or fading out expression wrinkles.